1. Field of the Invention
This invention relates generally to the analysis of an analyte in a solution and particularly to the preparation of a control solution for analytical tests for the presence of ketone bodies, for example, in biological fluids.
Ketone bodies are the common designation for the group of compounds including acetoacetic acid, .beta.-hydroxybutyric acid and acetone. Acetoacetic acid is a normal end product of fatty acid oxidation in the liver, and is also produced, to a very limited extent, by the oxidative breakdown of leucine, alanine and tyrosine. .beta.-hydroxybutyric acid is formed from acetoacetic acid by reversible reduction. Acetone is produced through nonreversible decarboxylation of acetoacetic acid: ##STR2##
Abnormally high amounts of ketone bodies in urine or blood are referred to as ketonuria and ketonemia, respectively. These abnormalities can occur as a result of such diverse conditions as diabetes mellitus and starvation. An example of the importance of monitoring the level of ketone bodies in such biological fluids is that detection of ketonuria in the diabetic may indicate the need for a change in insulin dosage (or other disease management procedure).
2. Background Art
Analytical procedures for determining the presence of sample constituents, whether gravimetric, volumetric, spectrophotometric or the like, should be evaluated periodically for reliability of results. Unless the reliability of such procedures is assessed, any data developed from them is meaningless. Therefore, devising and maintaining an appropriate analytical procedure must necessarily include quality control measures, for example, evaluation of experimental error produced by the procedure, or assessment of the training and efficiency of the technologist performing it. In other words, some means of predicting the dependability of the data produced by a person conducting the procedure is crucial to its successful use. In addition, it is desirable to have such controls available for training purposes.
The most efficacious and direct way to evaluate parameters such as reproducibility of results, sensitivity and accuracy of an analytical procedure, and to aid the training of technologists in the procedure, is to subject the procedure to a test sample wherein the presence and/or concentration of the substance being determined, or one which simulates the analyte, is known. Such a test sample is termed a control, and data furnished by the procedure can thereby be compared with known data to reveal discrepancies.
Exemplary of known analytical control devices is CHEK-STIX.RTM., a product marketed by the Ames Division of Miles Laboratories, Inc. It consists of various pads of bibulous carrier mounted on a strip of plastic, each pad being impregnated with one or more substances which, when dissolved in water, simulate pathological urine constituents. Accordingly, when a CHEK-STIX device is immersed in a premeasured volume of water for a predetermined time, a control solution results which simulates urine containing such metabolites as glucose, bilirubin, urobilinogen, ketone, occult blood, nitrite and protein. Such a control solution can, for example, be used to monitor the test devices known as N-MULTISTIX.RTM. and KETO-DIASTIX.RTM., both dip-and-read analytical devices marketed by the Ames Division of Miles Laboratories, Inc.
Another example of a control device is embodied by the product TEK-CHEK.RTM., also marketed by the Ames Division of Miles Laboratories, Inc. It comprises lyophilized urine containing natural and artificial additives to simulate both normal and pathological urine. In use, TEK-CHEK control device is added to a premeasured quantity of water to form the control solution.
The N-MULTISTIX and KETO-DIASTIX reagent test devices determine ketone bodies by the nitroprusside-ketone complexing phenomenon. When contacted with an aqueous ketone solution, the formation of a colored complex indicates the presence of a ketone; an estimate of the ketone concentration can be based on the intensity and hue of the color formed.
The aforedescribed TEK-CHEK control utilizes a pH indicator as a chemical substitute for ketone in lyophilized urine. The substitute is used because ketones are difficult to maintain in their natural state. However, while this chemical substitute is stable, its use in the control does not provide a positive test for ketones, but merely indicates the active presence of the base used in a ketone test.
U.S. Pat. No. 4,193,766, commonly assigned herewith, is directed to a device useful in the preparation of a ketone control solution. The device utilizes certain metal ion complexes of acetylacetone and its homologs as a substrate.
Many early ketone reagent tests were not specific for .beta.-keto acids. Accordingly, compounds such as .beta.-diketones or acetone were commonly used in controls for such tests, as these were known to be more stable, particularly under heat stress, than .beta.-keto acids. U.S. Patent Application Ser. No. 324,779 (continuation of Ser. No. 90,926), commonly assigned herewith, discloses a device for preparing a ketone control solution wherein sodium enolate derivatives of .beta.-keto esters are used. The device is, therefore, useful for the preparation of a control solution for ketone tests which are specific for .beta.-keto acids.